(i) Technical Field
A certain aspect of the embodiments discussed herein is related to a method for fabricating a semiconductor device, and is more particularly related to a method for fabricating a semiconductor device including a step of forming a gate insulating film on a GaN-based semiconductor layer.
(ii) Related Art
Field effect transistors (FETs) using a compound semiconductor containing Ga (gallium) and N (nitrogen) (GaN-based semiconductor) draw a lot of attention as devices capable of operating at high frequencies (radio frequencies) and outputting high power. The GaN-based semiconductor is a semiconductor that contains gallium nitride (GaN), and may be GaN, AlGaN, InGaN or AlInGaN. The AlGaN is a mixture crystal of GaN and AlN (aluminum nitride), and AlGaN is a mixture crystal of GaN and InN (indium nitride), while AlInGaN is a mixture crystal of GaN, AlN and InN.
A metal insulator semiconductor FET (MISFET) is known as an FET using the GaN-based semiconductor (see Japanese Laid-Open Patent Publication No. 2006-286942). The MISFET has a gate insulating film between a GaN-based semiconductor layer and a gate electrode. The gate insulating film of the MISFET suppresses leakage current between the gate electrode and the semiconductor layer.
However, the gate insulating film grown by a low-temperature growth method such as atomic layer deposition (ALD) may be etched by an alkaline solution used during a process. This may cause leakage current flow between the gate electrode and the semiconductor layer. Particularly, in a case where reverse leakage current from the gate electrode to the semiconductor layer caused by applying the electric field in the reverse direction concentrates on a faulty portion in the gate insulating film, the FET may be broken down or faulty. A similar problem may arise in CVD or sputtering.